Candidate allele & gene hypotheses developed from pharmacological & genetic findings are tested. Also, we follow up on whole genome linkage findings. Candidate gene linkage investigations included: DRD2 Ser311Cys and haplotype/alcoholism and opioid addiction, HTR1B/antisocial alcoholism, SLCA4/anxiety, SLCA4/OCD, HTT and severe serotonin-associated behaviors, BDNF Val66Met and episodic memory, NPY/anxiety, & COMT/opioid addiction/Schizophrenia/anxiety/dysphoria/Executive cognition, TPH2/anxiety-dysphoria, GABAA alpha 2 and alpha 6/alcoholism, and DISC1/schizophrenia. Phenotype, sampling framework, genetic structures [e.g. TDT, sibpairs], & power are evaluated. Assessment is generally by structured interview, & usually with intermediate phenotypes and/or additional end-phenotypes. The Finnish dataset was ascertained from criminal alcoholic probands & is thus enriched for Type II [early onset] alcoholism. SW Indian, Plains Indian, Ten Tribes, & Finnish datasets are derived from isolates; psychiatric interviewed controls are available from source populations. Chinese and German case/control datasets are in use as is a predominantly African American cocaine dataset [N=1000]. Remaining datasets are almost entirely Caucasian. Some 980 psychiatrically interviewed Caucasian population controls are available. The SW Indian dataset includes 600 sibpairs, the Finnish dataset used in the SLCA4 study included 366 sibpairs, & the Plains Indian EEG dataset contains a large number of sib & relative pairs. Both schizophrenia datasets [Egan & Weinberger, Malhotra] enable TDT/sTDT analysis. A publicly available portion of the COGA datset (Collaboration on the Genetics of Alcoholism) is also used. Power for case/control association is dependent on allele frequency, association strength, & desired level of alpha. Functional alleles tested have moderate [HTR2C, HTR2A, mu opioid receptor: 0.1] or high [SLCA4 & COMT: 0.4] frequencies, & functional polymorphisms known to affect alcoholism ADH2 Arg47His & ALDH2 Glu487Lys have 5-10 fold effects. Therefore, our smallest datasets [n=50] have 58% power at the p less than 0.01 level; power is essentially 100% for larger datasets available for alcoholism [several datasets], schizophrenia, OCD, anorexia nervosa, SAD, & bipolar. For lower effect size, power at p<0.01 remains > 0.8 for the association strength of 0.1, in the larger datasets. Relationship of candidate genes and alleles to behavior: DRD2. The DRD2 dopamine receptor, "Reward Deficiency Gene" hypothesis, was tested in SW Indians with three markers: the Taq1A marker previously implicated, an STR, & Ser311Cys, which impairs signal transduction & which is far more abundant [0.16] in this particular population as compared to Caucasians [0.03]. Because it impairs function, Cys311 is a surrogate for unknown DRD2 alleles that attenuate function to a similar extent or by the same mechanism [transduction]. There was neither sibpair linkage nor association, although the dataset included 15 Cys311/Cys311 homozygotes. Previously, we reported early negative results for DRD2 & alcoholism in ethnically matched, psychiatrically interviewed alcoholics & controls, in severe alcoholics, & in alcoholics with parental alcoholism. We identified large ethnic differences in DRD2 allele & haplotype frequencies, & helped discover Ser311Cys. The results suggest there is scant evidence for a substantial role for DRD2 variation in alcohol vulnerability. However, to monitor functional variants at DRD2, wedeveloped high throughput assays for Ser311Cys & -141DelT. With a ten-locus DRD2 haplotype, we find positive linkage to opioid dependence in two large datasets. Candidate alleles to behavior: Serotonin transporter. A functional serotonin transporter promoter polymorphism was associated with dimensionally measured anxiety. Quantitative linkage in 366 Finnish sibpairs linked this polymorphism to the two anxiety-related subscales of the TPQ [Mazzanti]. Function was further pursued by in vivo B-CIT SPECT imaging of transporter density. In controls [but not alcoholics], the lower transcribing s allele was associated with lower brain transporter density. Alcoholics experience sustained changes in serotonin transporter function, for example due to alcohol-induced serotonin release or effects of withdrawal. The polymorphism was linked to metabolic activity in amygdala induced by a cognitive fear challenge. A rare SERT missense variant was linked to severe psychopathology in two families. Discovery of a new common functional SERT HTTLPR allele enabled linkage to OCD in two populations. We built on findings from mouse genetic models to identify a potential role for the 5HT1B receptor in a subtype of alcoholism. HTR1B was implicated as an alcohol preference gene by a mouse alcohol preference QTL & subsequent discovery that the HTR1B knockout mouse exhibited increased aggression & preference for alcohol. As a terminal autoreceptor, 5HT1B modulates serotonin release & was an excellent candidate for variation in alcohol preference & aggressivity, independently of the mouse findings. Aggressive & impulsive behaviors are represented in two psychiatric diagnoses - ASPD & IED [Intermittent Explosive Disorder] & alcohol preference is a component of alcoholism. We studied 640 Finnish subjects included 350 sibpairs [220 unaffected, 79 discordant & 51 affected] & 418 Southwestern Indians including 305 sibpairs [223 unaffected, 71 discordant & 11 affected pairs] & classified for the presence/absence of antisocial alcoholism [DSMIII-R alcoholism plus either ASPD or IED]. In this single-locus study, evidence for i.b.d. linkage was found in both datasets [p=0.04 & p=0.01] & association to HTR1B was also detected in Finns. Relationship of candidate genes and alleles to behavior: TPH2 was linked to anxiety/dysphoria in multiple populations and the linked haplotype was shown to be associated with low serotonin turnover as indexed by 5HIAA levels, a DISC1 haplotype linkage to schizophrenia by Peltonen et al was replicated. COMT Val158Met & Frontal lobe function: Executive cognitive functions are thought to be impaired in several psychiatric diseases: alcoholism, ADHD, & schizophrenia (SZ). Patients with SZ, & to a lesser extent their healthy siblings, have deficits in working memory & show excess cortical activity [& are thus said to be inefficient] during these tasks. We found an allele-dosage relationship of a functional COMT variant to frontal cognitive function. The relationship is seen across several populations differing in baseline cognitive function: SZ, moderate-severe head injury, & controls. Dopamine enhances prefrontal cortical efficiency. Met158, a common COMT variant, leads to four-fold reduction in COMT activity & was thus an excellent candidate allele for frontal lobe cognitive function. Wisconsin Card Sort performance was evaluated versus COMT genotype in 75 controls, 184 SZs, & 222 siblings of SZs, with discovery of a remarkable allele-dosage relationship was found to perseverative errors in each group. This finding was replicated in controls and head-injured patients, and expanded by study of frontal metabolic activity during the N-back task. The Val158 allele was associated with increased metabolic activity in frontal lobe consistent with the hypothesis of diminished cortical efficiency. Val may have counter-advantages: in a two populations Met predicted anxiety in women and decreased frontal EEG coherence, and in two other populations the Met allele was associated with lower resiliency to pain/stress. The GABAA alpha 2 (chr 4 cluster) and alpha 6 (chr 5 cluster) recptors were linked to alcoholism. These linkages followed up our earlier whole genome scan in SW Inddians. The alpha 2 finding replicated the haplotype found by Edenberg and showed the linkage may be mediated through the anxiety dimension.